To call a spade a spade is to tell something as it is.
It’s an idiom that is urging people to be blunt, straight and honest.
Since the 20th century, however spade started to gain a second, slurry meaning, tainting the expression with racism.
“Call a spade a spade” came into the English language through Nicholas Udall’s translation of Erasmus in 1542.
Erasmus himself took the created the expression through paraphrasing a Greek saying; “to call a fig a fig and a trough a trough.”
It wasn’t until the 20th century, that white people in America started using the term spade for black people in a degrading manner.
This started taking off in the 1920’s, during the Harlem Renaissance, to mock upcoming black people.
“Call a spade a spade” is already a dying expression, that has been contaminated by offensive connotations and “tell it as it is” is much more effective in doing the idiom’s job without upsetting anybody.